Hydroformylation of olefinic compounds is a reaction of great industrial importance, and most of the processes employ catalysts that are dissolved in an organic phase that consists of reagents, products, and optionally excess ligands, even though problems arise in separating and recovering the catalyst, in particular when the latter is a noble metal, such as, for example, rhodium.
A solution for this problem was described in French Patent FR-2,314,910. The solution consists in carrying out the hydroformylation in the presence of an aqueous solution that contains a rhodium complex that is made water-soluble thanks to the presence of a sulfonated phosphine ligand which is itself water-soluble, such as the sodium salt of trisulfonated triphenylphosphine. In this way, the organic phase that contains the aldehydes is easily separated from the aqueous phase that contains the catalyst. The technique is the object of a considerable number of works that were discussed in an article by W. A. Herrmann that appeared in Angewandte Chemie International [Applied Chemistry International] in 1993, Volume 32, pages 1524 ff. Despite the great industrial advantage of this technique for hydroformylating propylene, a drawback of this two-phase system is that olefins are not soluble in water; this leads to relatively low reaction rates which make it impossible to use it for long-chain olefins.
Further described in U.S. Pat. No. 3,565,823 was a technique that consists in dispersing a compound of a transition metal in a tin salt or germanium salt and an ammonium salt or a quaternary phosphonium salt of formula (R.sub.1 R.sub.2 R.sub.3 R.sub.4 Z)YX.sub.3, in which R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are hydrocarbyl radicals that have up to 18 carbon atoms, Z is nitrogen or phosphorus, Y is tin or germanium, and X is a halogen, chlorine, or bromine, whereby this ionic-type non-aqueous medium constitutes a "molten salt." U.S. Pat. No. 3,657,368 described a process for hydrogenating olefins, and U.S. Pat. No. 3,919,271 described a process for hydrogenating nitriles that uses the preceding composition both with a tin and a germanium base. U.S. Pat. No. 3,832,391 claimed a process for carbonylating olefins by the same composition.
The compositions described above suffer from the drawback of having a relatively high melting point, while the hydroformylation reaction takes place at, for example, less than 90.degree. C.
French Patent Application No. 95/14147 of Nov. 30, 1995 proposed that it was possible both to keep the advantages of a two-phase application while avoiding the drawbacks that are associated with, on the one hand, the use of water and, on the other, with the use of compounds with a high melting point, by dissolving the catalytic compounds of transition metals of groups 8, 9, and 10 and in particular the compounds of cobalt, ruthenium, rhodium, iridium, palladium, and platinum, which are known for catalyzing hydroformylation, in organic-inorganic salts that are liquid at low temperature.